Pakistan on Wednesday headed for a political showdown as opposition leader Nawaz Sharif [Images] vowed to defy restrictions and go ahead with his planned massive 'Long March' to Islamabad [Images] on Thursday, even as authorities arrested hundreds of politicians and activists to thwart the protests.

"We want to change the outdated system and in the next seven or even in three days, we may change the destiny of Pakistan," a defiant Sharif thundered at a rally in Abbottabad in the North West Frontier Province.

Police and security agencies carried out massive raids and arrests of lawyers, political leaders and activists in an overnight swoop, which was still going on. They outlawed demonstrations in the capital as well as in the provinces of Punjab and Sindh, through which the rally is to proceed.

Top Opposition leaders, including Pakistan Muslim League-Nawaz Chairman Raja Zafrul Haq, were put under house arrest. Cricketer-turned-politician Imran Khan [Images], who heads the Tehrik-e-Insaf party, went into hiding to elude the security personnel who went to arrest him. So did the countless other eminent lawyers and political leaders.

Against the backdrop of the looming political confrontation, army chief General Pervez Kayani met Prime Minister Yousuf Raza Gilani [Images] to discuss the situation.

Official sources told private TV news channels that Kayani and Gilani discussed internal security situation and political issues. The meeting comes at a time when President Asif Ali Zardari [Images] is out of the country attending a summit meeting of the Economic Cooperation Organisation in Tehran.

The government also moved to refute media reports that Zardari was going to UAE and might not be present when the opposition march to press for reinstatement of judges sacked during the 2007 emergency takes place.

A political meltdown at this time, media reports have warned, could lead to some form of intervention by the country's powerful military, which has often stepped in to seize power when there is a political chaos.

The political confrontation in the country comes even as Islamabad is grappling with a surge in terror attacks and trying to fix an ailing economy which is afloat only, thanks to international donors.

Putting these points across, Sharif declared "I cannot rest when Pakistan is being taken on a disastrous course."

"We cannot compromise when all institutions are being ruined and the system is on the verge of collapse," the former Premier said.

Addressing thousands of his supporters, he told them that the country was in crossroads and it was time to defy restrictions to save the country.

The protesting lawyers, PML-N leaders and workers and some other political groups are demanding Zardari fulfill a pledge to restore Supreme Court judges sacked by former President Pervez Musharff during the emergency in 2007.

Zardari is resisting restoration sacked Chief Justice Iftikhar Muhammad Chaudhary as he fears that the reinstated judges could limit his powers and revive corruption cases against him.

The protesters have decided to march in smaller groups from different cities from tomorrow and then converge into a big march to Islamabad where they planned to hold a sit-in protest outside the Parliament building till their demands are met.